Jason Wang
2020-Dec-04 06:10 UTC
[PATCH net-next] tun: fix ubuf refcount incorrectly on error path
On 2020/12/3 ??4:00, wangyunjian wrote:> From: Yunjian Wang <wangyunjian at huawei.com> > > After setting callback for ubuf_info of skb, the callback > (vhost_net_zerocopy_callback) will be called to decrease > the refcount when freeing skb. But when an exception occurs > afterwards, the error handling in vhost handle_tx() will > try to decrease the same refcount again. This is wrong and > fix this by clearing ubuf_info when meeting errors. > > Fixes: 4477138fa0ae ("tun: properly test for IFF_UP") > Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > > Signed-off-by: Yunjian Wang <wangyunjian at huawei.com> > --- > drivers/net/tun.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 2dc1988a8973..3614bb1b6d35 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1861,6 +1861,12 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > if (unlikely(!(tun->dev->flags & IFF_UP))) { > err = -EIO; > rcu_read_unlock(); > + if (zerocopy) { > + skb_shinfo(skb)->destructor_arg = NULL; > + skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY; > + skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG; > + } > + > goto drop; > } > > @@ -1874,6 +1880,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > > if (unlikely(headlen > skb_headlen(skb))) { > atomic_long_inc(&tun->dev->rx_dropped); > + if (zerocopy) { > + skb_shinfo(skb)->destructor_arg = NULL; > + skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY; > + skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG; > + } > napi_free_frags(&tfile->napi); > rcu_read_unlock(); > mutex_unlock(&tfile->napi_mutex);It looks to me then we miss the failure feedback. The issues comes from the inconsistent error handling in tun. I wonder whether we can simply do uarg->callback(uarg, false) if necessary on every failture path on tun_get_user(). Note that, zerocopy has a lot of issues which makes it not good for production environment. Thanks